So I've been trying to diagnose the heat in my 69 Electra for a while now. The temperature is great and the fan blows strong. When I select HTR, the hot air blows strong from the heater vent on the floor. When I select VENT, the hot air blows strong from the vents up top. The DEICE setting, however, seems to split the hot air between the heater on the floor and vents up by the windshield. This results in less than ideal defogging on cold and humid days. I've been following my 69 service manual trying to make sense of the air pathways through the climate control system. It appears to me that the heater door has to be open for deice to work properly. So the hot air MUST enter the chamber before the heater vent on the floor and then be directed through the defroster door to get to the windshield. I am unfamiliar with these climate control systems, is the air supposed to be split in this way when the DEICE setting is selected? If this is not the case, maybe the defroster door is not opening completely and directing the air away from the floor heater properly? Looking for some advice as to what I should be looking for. I checked for vacuum leaks at the zone switch and upon testing, the deice setting seems to be providing vacuum to both the heater door and deice doors like my service manual says. Thanks everyone.